Hydraulic pump and circuit



Sept. 19, 1950 J. P. GOLDEN HYDRAULIC PUMP AND CIRCUIT Filed April 18, 1949 3 Sheets-Sheet l ismm uzmm m m m m 5533. 6 ma ic E s E23 mmwqig 'INVENTOR.

BY JOHN P. GOLDEN hum (Z 4 ATTORNEYS QQ via 8 wn m lm n l w WWW km N@ L M L 5 3 mw QQ m9 m, ww m R l R QJU \3 R w Sept. 19, 1950 J. P. GOLDEN 2,522,783

HYDRAULIC PUMP AND CIRCUIT Filed April 18, 1949 3 Sheets-Sheet 2 INVENTOR.

JOHN P GOLDEN BY ATTORNEYS Sept. 19, 1950 J. P. GOLDEN HYDRAULIC PUMP AND CIRCUIT 5 Sheets-Sheet 5 Filed April 18, 1949 INVENTOR.

JOHN P GOLDEN iii/ Patented Sept. 19, 1950 HYDRAULIC PUMP AND CIRCUIT John P. Golden, Columbus, Ga., assignor to 'Goldens Foundry & Machine Company, Golumbus, Ga., a corporation of Georgia Application April 18, 1949, Serial No. 88,122

This invention is concerned with a hydraulic pump and circuit of the type in which a liquid under pressure is supplied to a varying load, such as one or more rams, for actuatin the same, illustratively as employed in a cotton baling or like baling press.

One of the features of the invention is the provision of a hydraulic pump and circuit, in which the pump is provided with chambers which operate concurrently in the circuit during the initial operations of the load during which a relatively large quantity of liquid is being delivered at a relatively low pressure; together with an unloading apparatus automatically responsive to the pressure being delivered, whereby one of the pumping chambers is operationally disconnected from the circuit and permitted to idle when a pre-set maximum of this low pressure condition is exceeded.

Another feature of the invention is the provision of a hydraulic pump having multiple chambers of dilferentcapacities, the fluid from these pumping chambers being delivered through separate outlet valves into a manifold system, together with a pilot valve responsive to the pressure in the manifold system and effective to control the operation of an unloader valve, whereb to procure movement of this unloader valve when a maximum pressure exists during a low pressure stage of operation of the hydraulic circuit, wherewith to disconnect the discharge from one said forcing chamber and pass the effluent thereof to a reservoir and therewith unload the said forcing chamber.

A further feature of the invention is the provision of a pump and circuit system, including an unloader valve for determining the operation of the pump in response to the pressure in a manifold, togetherwith a pilot valve construction which does not respond to the normal pulsations in said manifold while the system is working under a low pressure condition and which responds when the pressure in said manifold attains a predetermined low pressure maximum and thereby procures operation of said unloader valve.

A, further feature of the invention is a hydraulic pump and circuit system in which the pump can operate under two different conditions of delivery, at large volumes with low pressure, or at small volume with high pressure; an unloader valve for determining the operation of said pump; a pluralit of rams; a ram control valve biased to prevent operation of at least one said ram while the system is at low pressure; and

12 Claims. ((31.60-97) pilot valves responsive to the existing pressure in the system, with one of the pilot valves eifective when a predetermined pressure is reached to procure operation of said ram control valve whereby to bring all of said rams into operation and to cause the said pump to continue to operate under the condition of high volume until a high reaction pressure again is present; the other pilot valve being effective when such high pressure is present to procure operation of said unloader valve whereby the pum is caused to operate at low volume and to supply all said rams for obtaining a predetermined high pressure in the individual rams and therewith a high pressure effect upon the load being served by the trams.

' With these and other features of construction as objects in view, as will appear in the course of the following specification and claims, an illustrative form of practicing the invention is shown on the accompanying drawings in which:

Figure l is a conventionalized diagrammatic layout of one form of construction, indicating the elements and conduit connections,

Figure 2 is an axial upright section through a pump cylinder, with the pump valve.

Figure 3 is an upright axial section through an unloader valve.

Figure 4 is an axial section through a pilot valve, illustratively that for supervisin the ram control valve.

Figure 5 is a side view of the sliding member of the pilo-t'valve of Figure 4.

Figure 6 is an upright section through a ram control valve.

In the conventionalized diagram of Figure 1, the pump structure is shown as having a bed In upon which are mounted bearingsfor the crank shaft I I which is driven from any suitable source of power (not shown) and having a crank pin l2 for the crank rod l3 which is pivoted to the sliding cross-head M mounted in the guides I 5 on the bed. As show in Figures 1 and 2, the piston rod l5 extends from the cross head M through the packing gland ll into the cylinder body l8 fixed to the bed Ill. The cavit IS in the cylinder body l8 (Fig) 2) forms a'first and larger pumping or forcing chamber having an inlet valve 20 connectingthis chamber to the inlet manifold 2|, and the outlet valve 22 for connecting the same to the outlet conduit 23. Within the chamber IS, the piston rod is has one part 24 of large diameter, and a second part 25 of smaller diameter, this smaller part passing through, a further gland 26 and into a second pumping or forcing chamber 2i which is shown as formed in a separate body piece is secured to the cylinder body i3. The second chamber 21 has a valve 29 through which liquid is admitted into the chamber 2i, and this second chamber 21 is also provided with an outlet valve 39 for controlling the efilux from this chamber directly to a conduit ill, which is a part of the delivery manifold 32.

A main reservoir or sump id is provided at a sufficiently low level to receive drainage from the pump unloader valve and from parts of manifold 32 and other parts: and serves as a dis charge point to which the liquid is delivered. It is illustrated as being located above the level of the rams R-l, R--2, and R3; and connected by gravity supply pipes Hill, 822 and the valve RV when correspondingly open, to the rams Ri, RF-S. It is customary, in many instances, to use so-called hydraulic oil as the liquid in the hydraulic circuit, for the reason that such oil is essentially non-compressible under the operatingconditions: and accordingly the liquid will be hereinafter designated as oil. Oil is drawn from the sump cm, for example, through a filter M, by conduit (l2 having a branch 43 connected to the inlet manifold 2!, and a branch 45 connected to the inlet manifold for the valve 29. It will be understood that the pump may have one Or more sets of cylinders 59, El, these being served from the manifolds 2|, Q5 and the illustrated form and delivering to the conduits 23,

While the larger pump chamber 59 for each of the cylinder sets is being employed for delivering oil to the rams, this oil is being forced out through the conduit 23 to the upper end of the control or unloader valve UV and then passes, as will be described in detail hereinafter, through a pipe 50 and a check valve 5| to the manifold 32. When this larger chamber is is unloaded, that is, when its action of supply is not desired, its effluent passes through conduit 23 to the upper end of the unloader valve UV, and then by pipe 52 back to the sump 46, thus unloading this larger chamber [9 and the source of power for the pump.

' As shown in detail in Figure 3, the unloader valve UV has a body 55, with end plates 55, 57 secured thereto. The upper part 58 of the bore in the body 55 has a smaller section than the lower part 553. The sliding valve has a cylindrical part ill closely fitting the part 59 and sealed by the packing and shock ring 6| which is pressed into the upper end of the larger bore 59. This sliding valve body also has a larger lower end flange 62 which closely fits the larger bore 5%! and acts as a hydraulic piston or actuator. The upper part of this sliding body is hollow and has a cyl ndrical portion 63 which closely fits the bore 58 and can either shut off passage of fluid from the bore 58 into the conduit 52, in the position shown in Figure 3 or, when the valve body 63 is in raised position, can cut off the flow of fluid into the conduit 50, while opening for flow to the conduit 52. Between the cylindrical portions at, 63 of the sliding valve body, parts are cut away as at 64 to permit the flow into the conduit 52. The spring 55 presses the sliding valve body toward a normal lower position. A control pipe ill leads to the lower valve head 51 with an opening therethrough so that oil pressure can be applied against the lower face of the flange 62, the head 5! being hollowed out so that the pressure thus applied is exerted over the entire end face of the sliding valve body. A discharge or release conduit H is connected to a port opening into the larger part of the bore 53 at a point normally above the flange 52, but lying opposite this flange and thus cut off when the valve body has been raised to its maximum upward position. The release conduit ll leads to the sump 40.

The manifold 32, during pumping, is at the prevailing pump pressure during the delivery stroke: that is, it varies from a lower to a higher pressure, and back, as the single cylinder set or the multiple cylinder sets operate, in well known manner. This manifold 32 is connected directly to a central ram 'R-Z, and indirectly to the side rams R-i and P.-3 through a ram control valve RV. In the illustrated form, two pilot valves PVl and PV-2 are likewise connected to the manifold 32 and are responsive to the pressure therein and serve respectively to control the ram control valve RV and the unloader valve UV.

A pilot valve construction is shown in detail in Figures l and 5. Two pilot valves are illustrated in Fig. 1, and these may be of identical construction. Each has an operation dependent upon the pressure in the manifold 32.

An upper body portion 83 has a circular hol low or cavity ill with a plane upper end surface 82. A passage or small bore 83 having a cylindrical wall extends the cavity 8! along the of the body .80 and is connected to a control branch conduit 84 leading to the manifold 32. A lower valve body member 85 is screwed into the upper body member fill, Figure 4, by its threaded upper projection 85 which has a conically concave recess, at its upper end forming a valve seat 37 having a larger effective area than that of the passage 35. This valve seat and the cylindrical hollow or cavity '36 extending downward therefrom are concentric in the valve body members. The upper loody member 8d has a port 92 located between the bore 33 and the valve seat 8'5 and leads to the control conduit 93 for pilot valve PVl Or conduit in for pilot valve PV2. The lowervalve body member 85 has a port iii! below the valve seat 81 and leading to the discharge conduit ll by its branch e1.

The valve member of the pilot valve is shown in Figure 5 as having a large cylindrical portion 95, a conical seat surface 95 of large effective area at its bottom, a spring engaging stub M, and a hollow upward extension 93 of small effective area which closely flts and is slidable as a piston in the passage 83 of the upper valve body memher 8!]. The body portion 95 is loose in the cavity 81, leaving an annular space for liquid flow. This extension 98 has a cross bore 991. The valve biasing spring Hill engages the stub 93 and the spring seat ill! which can be adjusted by the screw I02 having the lock nut me.

The ram control valve RV is shown in detail in Figure 6 as having a body Hi5 with the upper and lower end plates M6, iill. The valve body Hi5 has an upper bore I ill, of lesser diameter than the lower bore I09. The sliding valve member has a solid cylindrical portion HEB which closely fits the bore Hill. A lower flange iii closely fits the bore M39 and acts as a. hydraulic piston or actuator. Extending upwardly from the solid cylindrical portion I ii! is a hollow extension portion I I2 of the same diameter. Peripheral slots H3 are provided between the portions Mil, H2. A spring I M normally biases the sliding valve body for downward movement. The control conduit 93 communicates with a port H6 in the lower plate I01 so that oil under pressure therefrom can exert a lifting effort'over the entire lower end of the sliding valve member. Opening into the bore I09, near the upper end thereof, is a relief or discharge conduit II'I branched from the conduit II. The manifold 32 connects with a port I I8 which is closed off by the upper hollow cylindrical portion II2 of the sliding valve body, when this valve body is in its lower position, whereas this port II8 is opposite the slots II3 when the valve body has been raised. Whenthe valve body is in its lower position, as shown, the part H2 thereof uncovers a port H9 leading to a discharge or relief pipe I20 for returning the oil to the sump 40. The upper end plate I of the ram control valve RV communicates with conduits I22 respectively leading to the rams RI and R3.

A branch I25 of the pressure manifold 32 leads to the ram R2.

A branch I30 from the manifold 32 leads to a quick opening drain valve I3I which may be operated by the lever I32 to permit quick dis charge of the contents of the manifold 32, and associated conduits, through the conduit I33, to the sump 40. This valve I3I will also be illustratively assumed to be an over-pressure valve, operating automatically to prevent the pressure in the manifold32 from rising above 2500 lbs. per square inch in this illustrative form that is, the valve opens when such pressure is reached, to permit the excess to return to the sump 40.

The operation of this hydraulic pump and circuit, illustratively used in conjunction with a cotton baling press having the press box PB and movable platen MP,can be described as follows:

It will be assumed that the smaller portion 25 of the pump piston displaces one unit of fluid per working stroke, whereas the larger portion 24 of the piston operates in the chamber I9 to displace two units of liquid per stroke. Thus, when the two chambers are working concurrently, three units of fluid are being displaced. It will be assumed that the power for driving the pump shaft II is being supplied by a motor which is to operate at a normalload often horsepower maximum. The rams R.I, R2, M3 are fully retracted. The sump 40 contains oil. The pressure in the manifold 32 will be assumed to start at atmospheric. The sliding member of the unloader valveUV is in its lower position, as shown: and so is the sliding member of the ram control valve RV. The movable member of the pilot valves PVI and PV.2 is .in raised position. In general, it will be assumed that all conduits are full of oil.

With the baling chamber of. the press closed, the pump is started, and now delivers three units of oil per stroke of each of its cylinders. The oil (one unit per stroke) being pumped by the smaller portion 25 of each piston passes directly to the manifold 32 The oil (two units per stroke) being pumped bythe larger portion 24 ofthe piston passes through the conduit 23 to the upper end of the unloader valve. UV, thence through conduit 50, check valve to the manifold. 32. This manifold is cut off .at the :drain valve .I3I, softhat pressure is built up therein. The oil in the manifold 32 is stopped by the upper part II2 of the slidingmember in the ram control valve, and finds its outlet upwardly. in the conduit I25 so that it operates the 'ramQRA-fi, This is the so-called central ram ofthe cotton press. While the reaction pressure in mahifold 32 is gradually rising, itsjdelivery is going jto the ram R2 and therewith the platen or followblock of the baling press is being moved against the low resistance of the loosely packed cotton, for example: and this platen MP raises the movable elements of rams RI and R-=-3 while oil flows from the sump through the pipe I20,

into the body of ram control valve RV above the sliding member thereof, and thence by pipe I22 to these rams, thus keeping them full of oil.

The resistance of this cotton, during the compression, gradually rises until the pressure reaction from the ram R2 through conduit I25 causes the fluctuating manifold pressure 32 to rise at maximum to, say, 950 pounds per square inch. As the pressure manifold 32 rises, its effect has been transferred through the control conduits 84 to the upper end of the small extension 98 of each pilot valve body, but this body has remained within the port 83, although undergoing minor downward movements as the maximum pressure during each pulsation of the pump rises above, say, 900 pounds per square inch as determined by the setting of the valve spring I00. The extension 98 seals the port 83 so that no liquid movesfrom conduit 84 into chamber 8|: andthe valve 96 is free of the seat 81 so that the conduit 93 is at essentially the same pressure as conduit 9| i. e. it can drain back to the sump. Assume that this spring has been set in pilot valve PVI to permit the final maximum pressure in the manifold 32, for this lower pressure condition of operation, to be 950 pounds per square inch: and in pilot valve PV2 to be 1000 lbs. per square inch. At this pressure the cross passage 99 of the extension 98 is moved below the plane upper surface 82 in the pilot valve PV-I so that oil from the manifold 32 now passes through line 84, through the port 83 and the hollow extension 98 with the cross bore 9a thereof, into the chamber 8| around the valve body, thus, acting on the upper surface of this body portion 95 to force the same downward against the spring I00, until the valve surface 96 engages the valve seat 81 and closes the same. This closes off drainage through the port and conduit 9t back to the sump, and pressure can now continue to build up since pressure fluid introduced through 84 now acts on the entire upper surface of 95, in-. stead of only on the cross sectional area at the extension 98. The ratio of these areas is purposely made great, so that the valve 95, 96, when once seated, remains fixedly seated: and the pilot valve thus includes parts which serve to maintain the associated control valve, e. g. valve UV, in its operated position when the pressure in the manifold 32 drops. The oil under pressure in the chamber 8I can also pass through the port 92 to the conduit 93. The fluid, passing relatively slowly through the conduits 84 and 93, due to their smaller cross sections and the small cross section of the annular space between the valve portion 95 and the wall of the chamber 8|, now comes beneath the flanged end of the valve body in the ram control valve RV, and raises this body. During the first upward movement of the hollow cylindrical portion H2. the port II9 leading to the sump is shut off. Therewith, the action of rams R-I, R-3 in drawing oil through the conduits I22, the upper end of the ram control valve RV, and the conduit I 20 from the sump 40, is stopped; and any continued movement. of the rams establishes a relative suction, so to speak, on the unper end of the moving valve bodyof the ram control valve RV. At the end of its upward movement, this control valve now presents the slots H3 oppositethe ports H8, and oil from the manifold 32 can now flow also to the rams R-I and R3. The actual maximum pressure during the pumping cycle, in the manifold 32 now drops to about /3 of the previous value, or, say 325 pounds per square inch. The pilot valve PV-I remains in its lower position despite this pressure drop in manifold 32 because the lower pressure, at this time, acts on the entire upper surface of body 95 with a force still suflicient to overcome spring I00. Therewith, also, the pressure per square inch in the upper bore I08 of the ram control valve, and beneath the lower flange III thereof, is identical: but the lower surface of the valve is greater in section than the upper, and this excess area above the flange III has free drainage by conduit I Ill, and hence this valve remains in its raised position.

The pump continues to operate, delivering three units of oil per stroke'per cylinder, which acts in the three rams, until the pressure in the manifold 32 again rises to and beyond 950 lbs. per square inch. When this pressure reaches 1000 lbs. per square inch, which illustratively is the pre-set loading of thespring in the pilotvalve PV--2, the oil from the manifold 32, passing through conduit 80, to the pilot valve PV2, is now able to depress the sliding valve body in the pilot valve PV-2 until this valve opens as described for. valve PVI, and procures delivery of oil through the conduit lllto the unloader valve UV, and raises the sliding valve member therein. As this member raises, its upper portion 53 begins to open the port to the conduit 52, so that the. pressure of. oil from conduit 23 now has an escape by the conduit 52 back to the sump. Thus, the pressure within the upper part of the body of valve UV drops, and oil no longer flows through the conduit 50. and the check valve closes. The continued upward movement of this sliding valve body now closes the port leading to the conduit 50 and fully opens the conduit leading to the sump discharge 52. Under this condition, thelarger diameter ofpiston I0, operating in chamber l0, and delivering two units of oil per, stroke per cylinder, now is freed so that its delivery passes back to the sump, efficiently, without significant back pressure being developed upon the pump and its driving power source.

The pump continues to operate with its piston or pistons of smaller diameter 25, however, and these pistons, with a rate of delivery of one unit per stroke per cylinder, continue to build up pressure in the manifold 32, and therewith in the rams RI, R-2, R-,-,-3 while delivering liquid in smaller quantity at a successively higher pressure.

During the stage of operation while all of the fluid from manifold 32 was passing through the conduit I25 to ram R-Z, the pressure was building up by three units per stroke per cylinder to a pressure of 950 pounds per square inch, roughly corresponding to a little less than the maximum ten horsepower demand upon the driving motor. When the ram control valve RV is actuated, the same rate of delivery continues, initially from a pressure condition of about that which was employed at ram Rr 2 immediately before, and again the pressure builds up to about 1000 pounds per square inch, again representing about the maximum ten horsepower load upon the driving motor. At this time, the unloadin valve UV operates, .and the pump now begins delivery with its smaller piston diameter only, at a rate of one unit of .volume per stroke per cylinder, and operates to increase or boost the manifold pressure in manifold 32 above the 1000 pounds per square inch at which the unloading begins. This condition continues until the driving motor has again reached its maximum output, and the rams are operating at maximum pressure in excess of 2500 pounds per square inch. (Theoretically, with the stated factors, the top pressure would be 3000 pounds per square inch, but in practice it is customary to employ an over-pressure or relief valve I3l at say 2500 pounds per square inch: such a relief valve is old and well known in such systems.)

The operation has thus produced a maximum compression in the cotton present in the baling press, and this cotton is now tied. In order to release the press, and permit the platen to recede, the operator moves the lever I32, usually after shutting down the motor. The valve l3! now opens completely and discharges from the manifold 32 and thus from the ram R2 with a quick drop of pressure toward atmospheric. When the pressure falls below 1000 pounds per square inch in the manifold 32, fluid'has likewise been fiowing backward from the unloading valve UV through the conduit ,I0, so that this valve UV has been drifting toward its lower position. It will be noted that oil can enter the space in the larger bore 59 from the manifold 0| under this condition, this relief manifold pipe Ii having its lower end below the minimum oil level in the sump or reservoir 00. Also, the ram control valve RV has its sliding member drifting downward with discharge of oil backward through the conduit 93 to the pilot valve PVI, The rams RI, R2 and R,3 have been discharging back to the manifold 32 and thus through conduit I30, I33 to the sump: this flow is temporarily closed off for rams RI and R3, at the ram control valve RV, permitted discharge from the rams R-I and R.--3 through port H9 and conduit I20 occurs. It will be noted that as the sliding member in the ram control valve member RV moves downward, oil can enter the larger bore I09 from the conduit 1.

As the pressure in the manifold 32 continues to drop, ultimately the biasing springs I00 in the pilot valves force the bodies 95 upwardly until the extensions 98 have their cross bores 99 totally within the corresponding ports 83 and thus closed off. At this time, the oil from conduits I0, 93 can pass around the valve bodies. to the ports 00 and thus by conduit ill and relief conduit I I back to the sump.

Rams R-I, R-2, R3 go back to their initial position and the operator now moves the lever I32 to close the valve I3I. The system has now been restored to initial condition, and is ready for the compression of a new bale.

In the foregoing description of operation, the biasing spring of pilot valve PV-I was stated to have a lesser effect (e. g. to balance 950 lbs. per square inch in the manifold 32) than the biasing spring of pilot valve PV2 (e. g. to balance 1000 lbs. per square inch in manifold 32). It will, however, be noted that a similar staging operation can be effected if thesespring adjustments are reversed, so that the unloading valve first operates, and then the ram control valve. It is also feasible to have the system operate with the two valves moving simultaneously: but this condition is not preferred because it represents a momentary drop of the pump output to onethird of the initial delivery while simultaneously the effective cross sectional area of the rams is increased to three times the initial area provided by ram R--2: that is, the necessary ratio condition of the two valve seats in the pilot valve PV does not permit so delicate a control, and the pump isrunning at relatively low efficiency for the available maximum power, as it starts on this continuation of the cycle of operation.

It is obvious that the illustrative form of construction is not restrictive, and that the same might be made in many forms without departing from the scope of the appended claims.

What is claimed is:

1. A hydraulic system including a pump having multiple pumping chambers with inlet and outlet valves, a main conduit connected for directly receiving the liquid pumped from one of said chambers, a varying load device connected to the main conduit whereby varying back pressures are established in the main conduit, a second conduit and a valve device therein for selectively delivering to the main conduit the liquid pumped from another of said chambers and for discharging said latter liquid without passage to said main conduit, and a pilot device responsive to the pressure in the main conduit and connected to said valve device for procuring operation of the same from said delivering condition to said releasing condition upon the event that the pressure in said main conduit exceeds a pre-set maximum.

2. A hydraulic system as in claim 1, in which the said other pumping chamber has a greater capacity than said one pumping chamber, and in which the pilot device includes means for preventing reverse operation of said valve device until the pressure in the main conduit has been reduced essentially to atmospheric.

3. A hydraulic system including a pump having multiple pumping chambers with inlet and outlet valves, a main conduit for, directly receiving the liquid pumped from one of said chambers; a plurality of hydraulically operated load devices, of which one is directly connected to said main conduit, a first control valve for selectively connecting another of said chambers to said main conduit and for releasing the liquid pumped from said other chamber to a discharge point without passage to the main conduit, a second control valve for selectively connecting another of said hydraulically operated load devices to the'main conduit and for connecting the said other device to a discharge point, and pilot means responsive to the pressure in said main conduit and connected to said control valves effective to procure movement of said control valves when predetermined pressure conditions are attained in said main conduit.

4. A hydraulic system as in claim 3, in which said pilot means include selective devices for causing the first control valve to move from the position of connecting to said main conduit to the position of connecting to the discharge point when the main conduit pressure rises to a first value and to maintain the same in said latter position upon fall of the pressure in said main conduit, and also include selective devices for causing the said second control valve to move from the position of connecting to the discharge point to the position of connecting to the main conduit when the pressure therein again rises and attains a pre-set maximum.

5. A hydraulic system including a reciprocating pump having largerv and smaller pumping chambers with inlet and outlet valves, a main conduit ior directly receiving the, liquid pumpedirom the smaller chamber, an unloader valve and associated conduits for receiving the liquid pumped from the larger chamber and effective in one position of the unloader valve for delivering said liquid to the main conduit and effective in another position thereof for releasing said liquid to a discharge, a varying load device connected to said main conduit effective for determining the back pressure therein, said unloader valve having a hydraulically actuated piston for moving the same, a pilot valve structure having a part responsive to the pressure in the main conduit and a biasing device for preventing operative movement of the pilot valve until a pre-set pressure exists in the main conduit, a branch conduit from the main conduit and including said pilot valve and leading to said unloader valve piston for procuring movement of the same when the pilot valve is operated, said movement shifting the unloader valve from delivering to releasing position, said pilot valve structure including members of different efiective areas exposed to the pressure at the valve wherewith the member of smaller area is so exposed when the pilot valve is held biased by said biasing device and the member of larger area is so exposed when the pilot valve is in operated position.

6. A hydraulic system including a reciprocating pump having larger and smaller pumping chambers with inlet and outlet valves, a main conduit for directly receiving the liquid pumped from the smaller chamber, a plurality of hydraulic rams of which one is directly connected to said main conduit, a ram control valve effective in a first position for connecting another of said rams to the main conduit and in a second position for connecting the said other ram to a discharge point, said ram control valve having a hydraulically actuated piston for moving the same, a pilot valve structure having a port responsive to the pressure in the main conduit and :a biasing device for preventing operative movement of the pilot valve until a pre-set pressure exists in the main conduit, a branch conduit from the main conduit and including said pilot valve and lead ing to said ram control valve piston for procuring movement of the same When the pilot valve is operated, said movement shifting the ram control valve from said second position to said first position, said pilot valve structure including members of different effective areas exposed to the pressure at the pilot valve wherewith the member of smaller area is so exposed when the pilot valve is biased by said biasing device and the member of larger area is so exposed when the pilot valve is in operated position.

7. A hydraulic system including a reservoir, a power-driven pump with multiple pumping chambers connected for receiving liquid :from the reservoir, a main conduit connected directly to one of said chambers, an unloader valve selectively connecting another of said chambers to the main conduit and to the reservoir, two hydraulic rams of which one is connected directly to the main conduit, a ram control valve for selectively connecting the other ram to the main conduit and to the reservoir, said unloader and ram control valves each having a hydraulic actuator, a first pilot valve structure responsive to the pressure in said main conduit and effective when said pressure attains a first pre-set value to permit a first flow of liquid from the main conduit, a first pilot conduit for conveying said first flow of liquid to the actuator of said unloader valveyto cause the said unloader valve to move 'from'delive'ring to releasing position, said first pilot valve structure including a device for maintaining the same in said first flow permitting position, a second pilot valve structure responsive to the pressure in said main conduit and effective when said pressure attains a second pre-set value higher than said first value'to permit a second flow of liquid from said main conduit, a second pilot conduit for conveying said second flow of liquid to the actuator of the ram control valve to cause the ram control valve to move from the reservoir-connecting position to the conduit-connecting position, said pilot valve structures each including a drain connection to the reservoir efiective when the pressure in said main conduit falls below a pre-set minimum to cause the liquid moving consequent to said first and sec'ond'flows to move to the reservoir.

8. A hydraulic system including a reservoir, a

power-driven pump with multiple pumping chambers connected for receiving liquid from the reservoir, a main conduit connected directly to one of said chambers, an unloader valve selectively connecting another of said chambers to the main conduit and to the reservoir, two hydraulic rams of which one is connected directly to the main conduit, a ram con trol valve for selectively connecting the other ram to the main conduit and to the reservoir, said reservoir being connected and positioned for gravitational flow of liquid therefrom to said other ram, said unloader and ram control valve each having a hydraulic actuator, a first pilot valve structure responsive to the pressure in said main conduit and effective when said pressure attains a first pre-set value to permit a first fiow of liquid from the main conduit, a first pilot conduit for conveying said first flow of liquid to the actuator of said unloader valve to cause the said unloader valve to move from delivering to releasing position, said first pilot valve structure in-' eluding a device for maintaining the same in said first flow permitting position, a second pilot valve structure responsive to the pressure in said main conduit and effective when said pressure attains a second pre-set Value higher than said first value to permit a second flow of liquid from said main conduit, a second pilot conduit for conveying said second flow of liquid to the actuator of the ram control valve to cause the rain control valve to move from the position permitting gravitational flow from the reservoir to the position of connecting said other ram to'the main conduit, said pilot valve structures each including a drain connection to t-he'reservoir effective when the pressure in said main conduit falls .below a pre-set minimum to cause the liquid moving consequent to said first and second flovvs to move to the reservoir.

9. A hydraulic system comprising a pump and means for driving the same, said pump having larger and smaller pumping structures, a reservoir from which the pumping structures draw liquid, a main conduit in direct communication with the smaller pumping structure, an unloader valve connected with the larger pumping structure and having selectively connectable outlet ports leading respectively to the main conduit and to the reservoir, said unloader valve having an actuating cylinder and piston, a hydraulically operated variable load connected to said main conduit for supply therefrom, a pilot valve connected to said main conduit and having selectively connectable valve ports leading respectively to the said cylinder and to saidreservoir;

said pilot valve including valve seats and "a mavable member having a part of small area and another part of larger area, said parts selectively engaging a first and a second of said valve seats when the valve member is moved whereby in one position of the valve member the part of small'area is exposedto the pressure in the main conduit and fiow from the main conduit is stopped at a first'valve seat and the member permits fiow from the said cylinder-connected port past another valve seat to the reservoir-connected port, and whereby in another" position of the member the port of larger area is held to the second valve'se'at by said pressure and there with "the reservoir-connected port is closed and liquid can flow past the said first seat to the cylindergconnected port; a valve for discharging said m'ain conduit to the-"reservoir whereby to reduce the pressure in said main conduit, and means for moving the member toward said one position when the pressurein said main' conduit is below a pr'e-set minimum. 7 g

10. A hydraulic system including a pulsating pump and means for driving the same, a 'vari-' able load device, a main conduit connecting the pump and the load device, means including a control valve and effective for controlling the rate of movement of the load device, said control valve having an -actuating cylinder and piston, and a pilot structure for procuring operation of the control valve; said pilot structure including a valve body having a hollow and also having connected to the hollow a small here with a port connected to the main conduit, a sliding valve member having a small cylindrical part engageable in the small bore at a first end portion of the member whereby to close the bore and receive a small force for moving the member along said small bore, said member having also a larger part located in said hollow and said body having a valve seat for receiving said larger partin a second end position of the member, said body having a second port opening to said hollow and effective for releasing pressure fluid from the body, said body having a third part opening to said hollow at a point between said bore and said valve seat whereby said larger part and its valve seat control flow between said second and third ports, said third port being incommuiiication with said cylinder and in selective "communication with the second port and with said bore in the said first and second end positions of the member, and a spring acting on the sliding memberfo'r' urging the'small part into closing position in said bore;

11. A hydraulic'sy'stem as in claim 10, in which the small port has an axial hole and a transverse hole leading therefrom to its periphery, said transverse hole being positioned within the bore in said firstend position and thereby closed against flow therethrough.

12. A hydraulically responsiveva'lve having a body with a cavity with axially arranged smaller and larger portions and a bore having a terminal connection, a valve member slidable in said cavity and having a small cylindricalex'tension at one end and a larger seating surface at the other end, said bore closely receiving said small extension whereby said bore and extension act as cylinder and piston in response to pressure at said terminal connection, said body having a valve seat for receiving said seating surface whereby to close off saidlarger and smaller poi tions of the cavity from'one another,'a port open ing to the larger portion of the cavity, and a port JOHN P. GOLDEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 914,167 Nelson Mar. 2, 1909 947,613 Gathmann Jan. 25, 1910 1,261,043 Luce Apr. 2, 1918 10 1,847,889 Osborne Mar. 1, 1932 1,982,711 Vickers Dec. 4, 1934 

